Let →u=^i+^j,→v=^i−^j and →w=^i+2^j+3^k. If ^n is a unit vector such that →u.^n=0 and →v⋅^n=0, then |→w⋅^n| is equal to:
A
1
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B
2
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C
3
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D
0
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Solution
The correct option is D 3 Let ^n=x^i+y^j+z^k, where x2+y2+z2=1. Now, →u.^n=0(^i+^j).(x^i+y^j+z^k)=0x+y=0−−−(1) Also, →v.^n=0(^i−^j).(x^i+y^j+z^k)=0x−y=0−−−(2) Solving (1) and (2), we get x=y=0. Thus z=1or−1 (because x2+y2+z2=1 Thus, →w.^n=(^i+2^j+3^k).(±^k)=±3